Well, mine was done years ago, removed assembly,cut large flap,peeled back,busted up and emptied, welded back flap. Then about once every 2 months I would get p0420 insufficent catalyst.I thought, really?,you dont say,huh... Now I have done the good old tried and true spark plug non fouler trick. No CEL for over 6 months. I am well aware there will be nay sayers among us, but this is not the first time this trick has been used. It is as old as the downstream o2 sensor, and works very well.